Control unit for an electric motor, in particular fora fan motor

ABSTRACT

The invention provides a control unit for at least one electric motor, wherein the control unit performs open-loop or closed-loop control of the motor speed of the electric motor in such a way that in the case of control values in specific ranges which are typical of a fault when the setpoint value is being predefined, such a fault being, for example, a line break, a voltage failure or a short circuit, the control unit drives the motor with a predefined setpoint value which differs from the current control value.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 12/299,426, which was filed on Nov. 30, 2008 which claims thebenefit of priority of International Patent Application No.PCT/EP2007/054301, filed on May 3, 2007, which in turn claims priorityto German Patent Application No, 20 2006 007 136.9, filed May 4, 2006,The entire text of International Patent Application No.PCT/EP2007/054301 and German Patent Application No. 20 2006 007 136.9are hereby incorporated herein by reference in their entireties.

DESCRIPTION

The invention relates to a control unit for an electric motor. Suchcontrol units are used to perform open-loop or closed-loop control ofthe motor speed. In many cases, in particular in fan applications, themotor speed is lowered according to demand in order to reduce theconsumption of electric power. In the case of a fan, not only the powerdemand but also the flow noise are highly dependent on the motor speed,Referring to FIG. 8A and FIG. 1, FIG. 1 shows the shaft power output (1)of the fan motor 100 and the flow noise (2) of the fan 106 as a functionof the motor speed. The torque demand of a fan wheel 106 increases tothe power of two of the motor speed. As a result, the shaft power outputof the motor 100 even increases to the power of three of the motorspeed. This means that, for example, at half the motor speed the outputpower of the motor 100 only reaches 12.5% of the rated power. The shaftpower output even drops below 1% if the motor speed is less than 21.5%of the rated motor speed. The flow noise (2) has been found empiricallyto drop to 15-17 dB(A) when the motor speed is halved.

In addition to the energy demand, the noise can therefore also besignificantly reduced if motor-speed-controlled fan motors are used andif open-loop control of the motor speed and therefore of the air line isperformed according to demand. The motor speed of a fan can beinfluenced in different ways as a function of the types of motor used.In the case of direct current motors, open-loop control of the motorspeed is performed by means of the motor voltage. The control unit canpredefine the motor voltage with a clocked voltage converter (chopper)or by means of a controlled rectifier, For universal motors, theamplitude of the alternating voltage can be set by means of a phaseangle controller. In the case of a brushless motor (also referred to asBLDG or electronically commutated motor, referred to as EC motor), thecontrol unit performs the electronic commutation. The control unit canadditionally influence the motor voltage and as a result the motor speedthrough corresponding clocking of the transistors in the commutationelectronics. In the case of asynchronous motors, either the frequencyand the amplitude of the motor voltage are predefined with a frequencyconverter, or in the case of cost-effective systems, in particular inthe case of fan drives, only the motor voltage is changed, for example,by means of a phase angle controller (referred to as slip controller).

The desired motor speed is usually defined by means of superimposedopen-loop control. The setpoint value of the motor speed is oftentransmitted with an analogue value (for example 0-10 V) or with apulse-width-modulated, digital value (PWM). FIG. 2 shows an inputcharacteristic which is typical of fan applications. In this example,the superimposed controller has to output 0-10% of the control signal(x) for the motor to be stationary (nsetp=0). A disadvantage of thismethod is that in the case of faults, for example in the case of a linebreak or a short circuit in the control line, the fan can stop. In thiscase, it is not possible to ensure sufficient cooling, which may lead toa failure of the system. As a result, considerable material damage mayoccur and large losses due to a failure of production.

SUMMARY OF THE INVENTION

The present invention is therefore based on the object of configuringthe input characteristic of the control unit in such a way that in thecase of such a fault the motor continues to operate with a predefinedmotor speed. In the case of a fault such as a line break or a shortcircuit in the control line or in the case of the failure of thesuperimposed controller, the probability is high that the control signalx will record the value 0% or 100%,

According to the invention, the customary input characteristic istherefore changed according to FIG. 2 in such a way that in the case ofinput values in specific ranges, primarily approximately 0% or 100%, thecontroller drives the motor with a predefined setpoint value whichdiffers from the current setpoint value.

In one advantageous embodiment, the controller additionally outputs awarning in the case of such a fault. This warning can be output by meansof a visual or audible signal, by means of an analogue or digitalelectronic signal or by means of a commutation bus, for example, CANbus.

BRIEF SUMMARY OF THE DRAWINGS

In the figures:

FIG. 1 shows the shaft output power of the fan motor and the flow noiseof the fan as a function of the motor speed;

FIG. 2 shows an input characteristic which is typical of fanapplications;

FIG. 3 shows the input characteristic of the control unit in anadvantageous embodiment;

FIG. 4 shows the inventive input characteristic of the control unit if asetpoint value of nsetp=75% is used when such a fault is detected;

FIG. 5 shows the program sequence for implementing the inputcharacteristic curve;

FIG. 6 shows a exemplary circuit;

FIG. 7 shows a further exemplary circuit with a warning output;

FIG. 8A is an isometric view of a fan that may be operated by a motorcontrolled by a control unit in accordance with present invention; and

FIG. 8B is an isometric view of a pump that may be operated by a motorcontrolled by a control unit in accordance with present with presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 shows the input characteristic of the control unit in anadvantageous embodiment. in this example, the superimposed controllermust output 5-10% of the control signal (x) instead of 0-10% in order tostop the motor. In the case of an analogue control signal (0-10 V) thismeans that in the case of a control voltage of 0.5 V to 1 V the motor isstationary (nsetp=0). A control voltage of less than 0.5 V indicates afault (for example a failure of the superimposed controller, a linebreak or a short circuit in the control line). When a setpoint value ispredefined with a PWM controlled digital signal, the motor will bestationary given a control signal of 5 to 10% PWM. A PWM factor of lessthan 5% means a fault. This is the case, for example, if the controlsignal is continuously at a low level (corresponds to 0% PWM). In thiscase, a predefined setpoint value of the motor speed is used. In FIG. 3,this value is for the fault nsetp=100%. For applications such as, forexample, with fans, reliable operation is therefore ensured even in thecase of a fault in the transferring of setpoint values, Although in fanapplications, the power and noise are not reduced when such a faultoccurs, sufficient cooling is ensured.

A setpoint value which differs from the maximum (100%) setpoint value ofthe motor speed can also be used in the event of a fault. In some cases,a reduced motor speed is sufficient for cooling in a normal situation,and the maximum motor speed (100%) is provided only for specificexceptional situations, for example for the failure of one of the fanswhich operate in parallel. FIG. 4 shows the inventive inputcharacteristic of the control unit if a setpoint value of nsetp=75% isused for the detected fault. This value is therefore used if the controlsignal assumes x values in the ranges 0-5% and 95%-100%.

In order to implement an input characteristic curve according to FIG. 4,the analogue control signal can firstly be converted into a digitalvalue using an analogue/digital converter. The signal is then furtherprocessed in digital form. In one advantageous refinement of theinvention, this can be carried out by means of a programmable componentsuch as a microprocessor, digital signal processor (DSP) ormicrocontroller. The programme sequence for implementing the inputcharacteristic curve is illustrated in FIG. 5.

In a further refinement of the invention, the input characteristic curveis implemented using an electronic analogue circuit. FIG. 6 shows anexemplary circuit for this. This circuit is composed of four analoguecomparators (K1 to K4), two operational amplifiers (V1, V2), two digitalNAND gates, and of an analogue multiplexer (MUX). The comparatorscompare the control signal X with the voltage values at thediscontinuities in the input characteristic according to FIG. 4, that isto say with 0.5 V, 1. V, 9 V and 9,5 V. These voltages are produced herefrom the 10 V supply voltage with a resistor series. The output signalsof the comparators are further processed with the NAND gates and controlthe analogue multiplexer, as is shown by the following table.

Control signal X K4 K3 K2 K1 A1 AO Y 0 . . . 0.5 V 1 1 F 0.5 . . .1 V 10  0 V 1 . . . 9 V 0 0 9X − 1 V 8 9 . . . 9.5 V 0 1 10 V 9.5 . . . 10 V0 0 1 1 1 1 F

F is here the predefined setpoint value for the fault. If this value is,for example, 75%, as in FIG. 4, 7.5 V has to be connected here.

This circuit can be supplemented with a warning output (W), asillustrated in FIG. 7. In a normal situation this output supplies alogic “1” and in the case of a fault it supplies a logic “0”. Thiswarning is output if the control signal X assumes values lower than 0.5V or higher than 9.5 V.

Referring to FIGS. 8A and 8B, the control unit 102 according to theinvention can form a separate unit or can be integrated into the motorhousing or into the terminal box of the motor 100 so that motor 100 andcontrol unit 102 form one mechanical unit. The solution according to theinvention can also advantageously be used in compact fans where controlunit 102 and motor 100 are integrated parts of the compact fan. Thesolution according to the invention can, however, be used not only infans, blowers and pumps 108 but also in any application in which in theevent of a fault it is more favourable to operate the motor 100 with apredefined motor speed than to switch off the motor 100.Correspondingly, the invention is not only limited to the illustratedand described exemplary embodiments but rather also comprises allembodiments of like effect within the sense of the invention.

As one example, a brushless DC motor that incorporates aspects of theinvention disclosed herein can be used to spin one or more hard disks inoperative relation to at least one read/write head inside of a cleanroom environment that is manufactured to HIM industry contaminationstandards. As another example, the motors disclosed herein can be usedto move storage media in other information storage devices such as, forexample, an optical disk drive, a magneto-optical disk drive, a tapedrive or a VCR.

1-14. (canceled)
 15. A cooling fan, comprising: a housing; a brushlessDC motor mounted in the housing; a fan wheel operatively engaged with arotor of the brushless DC motor, wherein the fan wheel is adapted torotate when the brushless DC motor is operated in order to create a flowof cooling air; a motor controller mounted in the housing in a fixedrelationship with the brushless DC motor, wherein the motor controlleris adapted (a) to cause the rotor and the fan wheel to rotate at anonzero speed if the magnitude of a control signal is in a range ofvalues associated with a fault condition and (b) to stop rotation of therotor and the fan wheel if the control signal is between a nonzero firstthreshold value and a second threshold value greater than the firstthreshold value.
 16. The cooling fan of claim 15, wherein the range ofvalues associated with the fault condition is a range from zero to thefirst threshold value.
 17. The cooling fan of claim 15, wherein thecontrol signal is one of a pulse-width modulated signal and a voltage.18. The cooling fan of claim 15, wherein control signal is an analogvoltage signal.
 19. The cooling fan of claim 18, wherein the range ofvalues associated with a fault condition includes a value thatrepresents one of zero volts and a voltage identical to a supplyvoltage.
 20. The cooling fan of claim 15, wherein the control signal isa modulated signal and the range of values associated with a faultincludes a value associated with a signal modulated 0% and a valueassociated with a signal modulated 100%.
 21. The cooling fan of claim15, comprising an analog-to-digital converter adapted to convert ananalog control signal into a digital control signal.
 22. The cooling fanof claim 15, wherein the first threshold value is one of 0.5 volts and5% modulation.
 23. The cooling fan of claim 22, wherein the secondthreshold value is one of 1 volt and 10% modulation.
 24. The cooling fanof claim 23, comprising a further circuit to generate a warning signalif the control value indicates a fault.
 25. The cooling fan of claim 24,wherein the further circuit generates one of a visual warning signal, anaudible warning signal, and a combination thereof.